Just recently I purchased an AirPort Epress from Apple to connect it to my stereo and enjoy music in a better quality than from the built-in speakers of the MacBook. The inital setup went fine but iTunes was not able to connect (iPhone just worked). After trying various things it turned out that IPv6 was responsible for this. Unfortunately it is not possible to turn IPv6 off in the GUI (brilliant idea, folks!). But it can be achieved via the command line. So here are the steps I had to take

• Open terminal
• Run: networksetup -listallnetworkservices
• Your wireless network probably shows up as “Wi-Fi“. Please adjust the following line accordingly, if your system uses a different name
• Run: sudo networksetup -setv6off "Wi-Fi"

With those steps things worked immediately.